Telephone-exchange system.



PATENTED NOV. 15, 1904.

H. G. WEBSTER.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED FEB. 4.1903.

NO MODEL.

Patented November 15, 1904.

UNITED STATES PATENT OFFICE.

HARRY G. \VEBSTER, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE STROM- BERC-CARLSON TELEPHONE COMPANY, OF ROCHESTER, NE\V YORK,

A CORPORATION OF NEIV YORK.

TELEPHONE-EXCHANGE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 775,226, dated November 15, 1904.

Application filed February 4, 1903. Serial No. 141,886. No modeLl To a who/1t it nuty concern;

Be it known that I, HARRY G. 'nns'rnn, a

citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented a certain new and useful Improvement in Telephone-Exchange Systems, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawing, form- IO ing a part of this specification.

My invention relates to telephone-exchange systems, and more particularly to such systems in which a source of current located at the central station may be employed for the purpose of supplying talking-current to substation transmitters.

The principal objects of my invention are to provide a telephone-exchange system in which the complicated cutoff mechanism heretofore employed may be dispensed with and a system having an improved means whereby the operator may test the operative condition of a subscribers line.

A further object of my invention consists in the provision of means whereby the disagreeable clicks produced in a subscribers receiver, due to changes in the electrical circuits of the corresponding line, may be reduced.

I shall describe my invention by reference to the accompanying drawing, in which are diagrammatically illustrated subscribers substations A and B, connected each by limbs 1 and 2 of a telephone-line with a central exchange at C. Each subscribers substation apparatus comprises a switch-hook 3, adapted when in its normal position to connect a signal-receiving means, such as the bell 4 and a condenser a, in series with the limbs of the telephone-line. \Vhen in its alternative or upper position, the switch-hook closes the change and there through the winding of a line-relay 9 to the negative pole of a common battery 10, adapted to supply talking and signaling currents used in the operation of the system. The limb 1 from each substation is also permanently connected with the tipsprings 11 of an answering-jack 12 and multiple calling-jacks 13 13. The limb 2, running from each substation, is normally serially connected, through the differentially-wound coils 14 and 15 of the cut-off relay 16, with the positive grounded side of the common battery 10. The common terminal of the relay-coils 14 and 15 is permanently connected with the sleeve-contacts 17 17 of the answering and multiple callingacks. These sleevecontacts 17 17 also constitute the testing-thimbles of the jacks.

The line-relay 9 is provided with an armature 18, adapted, when attracted by the relay 9, to close a local circuit from the battery 10 through the line-signal 19, which signal may be in the form of a small incandescent lamp. The local circuit through this signal-lamp also includes an armature 20 of the cut-off relay, the attraction of this armature 20 from its back contact serving, however, to open the circuit through the signal-lamp 19. The cutoff relay 16 is further provided with a second armature 21, adapted when attracted to shortcircuit the winding 14. of the relay, thereby connecting the line-limb 2 directly with the associated sleeve-contact 17 without theintervention of inductive resistance.

The operators cord-circuit may desirably comprise answering and calling plugs 22 and 23, whose tip and sleeve contacts are respectivel y connected by the cord-strands 2e and 25.

The usual ringing and listening key 26 is provided, a manipulation of which in onc'direction serves to connect the operators telephone set 27 in bridge of the cord-circuit and a manipulation of which in the reversed direction serves to connect the ringing-generator 28 in bridge of the cord-circuit.

The cord-strand 2% is electrically continuous through supervisory relays 29 and 30,

these relays being shunted by a condenser.

1 conductor 32 connects the common terminal of the relays 2 9 and 30 with the negative pole of the common battery 10. A supervisory controlling relay 33 is connected between the negative side of the battery 10 and the sleevestrand 25 of the cord-circuit. The armature 3 1 of this supervisory controlling-relay when attracted connects the positive pole of the battery 10 with supervisory signal-lamps 35 and 36, the circuits through these supervisory signal-lamps being respectively completed by the armatures 37 and 38 of the supervisory relays when in their normal unattracted positions.

An impedance-coil 39 is connected between the negative pole of the battery 10 and the terminal of the generator 28, adapted for connection with the sleeve-strand 25 of the cordcircuit.

The operation of my improved system will now be made apparent.

A subscriber at substation A upon removing his receiver from its switch-hook closes a continuous electrical circuit between the limbs 1 and 2 of the associated telephone-line, thereby permitting the passage of current from the battery 10 through the line-relay 9 to telephone-limbs 1 and 2 and through the two differentially-wound coils of the cut-off relay 16. Acurrent flowing through this circuit causes the energization of the line-relay 9 to attract its armature 18. The armatures 20 and 21 of the cut-off relay are not attracted by current flowing through this circuit,for the reason that the coils 14 and 15 are difierentially wound, thereby producing no appreciable net energization of the core of the cut-ofi relay. The armature 20 when in its unattracted position serves to close, in connection with the attracted armature 18, a local battery-circuit through the line-signal19, causing this signal-lamp to glow, thereby notifying the operator that the subscriber at substation A desires connection with some other subscriber. She thereupon inserts an answering-plug 22 within the corresponding answering-jack 12. A circuit of decreased resistance is thus closed through the coil 15 of the differential relay, this circuit being traced as follows: from the negative pole of the battery 10, through the supervisory controlling-relay 33 to the sleeve of the plug 22, to the sleeve-contact 17 of the answering-jack 12, through the coil 15 of the differential relay to the positive pole of the battery 10. The increased flow of current through the single coil 15 causes a net energization of the cut-off relay, thereby causing the attraction of its armatures 20 and 21. The attraction of the armature 20 produces a break in the local circuit through the signal-lamp 19, whereby this lamp is extinguished. The attraction of the armature 21 causes the closure of a low-resistance circuit in shunt of the winding 1A of the differential relay 16 and 1 also serves to directly connect the sleeve-contacts 17 with the limb 2 of the associated telephone-line without the intervention of ind uctive resistance. This feature of my invention gives a talking-circuit between the springjack and the limbs of the telephone line, which being free from inductive resistances is peculiarly suitable for the transmission of voice-currents.

As previously pointed out, the insertion of the plug 22 within the answeringjack 12 causes the closure of a circuit through the supervisory controlling-relay 33, whereupon the armature 34: is actuated to connect the positive side of the battery 10 with the lamps 35 and 36. The receiver at substation A being ofi' its hook a circuit may be traced as follows: from the negative pole of the battery 10 through the relay 29, to the tip-strand 24 to the tipspring 11 of the answering-jack 12, to the limb l of the telephone-line, through the transmitter 5 and primary coil 6, to the limb 2 of the telephone-line, through the'short circuit in shunt of the coil 14, through the coil 15 of the differential relay to the positive pole of the battery 10. The core of the supervisory relay 29 being thus energized causes the attraction of its armature 37, whereby a circuit through the supervisory signal-lamp 35 is opened. The operator manipulates he'r ringing and listening key in the usual manner, connecting her telephone set in bridge of the cord-circuit, whereupon she ascertains the number of the substation with which the subscriber at substation A desires connection. Supposing this to be station B, she thereupon inserts her calling-plug 23 within a multiple jack 13 and manipulates her ringing-key to connect the generator 28 across the cordstrands 24 and 25 leading to the calling-plug 23, whereby a signaling-current is caused to actuate the call-bell 4 at substation B. The insertion of the calling-plug 23 within the jack 13 causes the closure of a circuit through the coil 15 of the differential relay 16 associated with the line running to substation B.

The armatures of this relay are thereby attracted, causing in one instance a break in the local circuit through the associated line signaling-lamp 19 and in the other instance the closure of a shunt-circuit of low resistance about the winding 14 of its own cut-01f relay. Upon answering the call the subscriber at substation B removes his receiver from its hook,

l thereby closing a circuit between the limbs of the associated telephone-line, which circuit includes the battery 10 at the central station, the associated line-relay 9, and the coil 15 or the associated cut-off relay. The consequent energization of the line-relay does not cause the illumination of the line signal-lamp 19,

e for the reason that the circuit through this lamp is open between the armature 20 of the cut-ofi relay and its back contact.

It will be remembered that the insertion of the answering-plug 22 in the answering-jack whether or not the called line is busy. In or- 12 caused the attraction of the armature 3 L, whereby-a circuit is closed through the supervisorysignaling-lamp 36 and the armature 38 of the supervisory relay 30. This lamp 36 will continue to glow until the removal of the I receiver from the switch-hook at the called substation. The removal of this receiver causes the closure of a circuit through the supervisory relay 30 similar to that previously traced for the supervisory relay 29, whereupon the armature 38 is attracted from its back contact, thereby causing a break in the circuit through the supervisory signal-lamp 36. Thus upon the extinguishment of the lamp 36 the operator receives a signal that the subscriber at substation B has answered the calling-signal.

It may be pointed out that the function of the impedance 39 is to prevent the opening of the circuit through the coil 15 of the differential relay associated with the line to substation B upon the connection of the generator 2b with the cord-circuit. The circuit through the relay-coil 15 may be traced during the connection of the generator with the cord-circuit through the impedance-coil 39 instead of through the supervisory controlling-relay 33, while a generator-circuit in shunt of the circuit through the calling-bell 1t and the condenser 4 at substation B is provided. This shunt-circuit being of comparatively high resistance and high self-indnction, the proper actuation of the calling-signal is not materially affected.

The means employed for testing a line to ascertain whether or not it is in use before a connection therewith is made may be described as follows: It will be seen that the test-thimbles associated with an idle line-f0r instance, the line leading to substation Bare normally connected with the positive grounded side of the battery through the coil of the differential relay. There being no current-flow through this idle line or the coil 15 the test-thimbles are normally of the same zero-potential as the grounded side of the battery 10. Upon the insertion of the callingplug within any one of the multiple jacks associated with this line to substation B an electric circuit is closed through the associated cut-otl-relay coil 15 and the supervisory controlling-relay 33. flowing through this circuit there is a consequent rise in the potential of all of the thimbles of the multiple jacks connected with this circuit. Therefore when the tested line is busy or has already been called by another operator at some other one of the positions on the multiple board the test-thimbles associated with that line will have been raised in potential above the normal potential of the ground ed side of the battery 10.

the calling-plug is used in connection with the test-thimbles of a called line to learn On accountof the current The tip-contact of der to test a line, the operatormanipulates her listening-key, thereby connecting her telephone set in bridge of the cord-circuit and by means of the contact l0 connecting the tip-strand 2% of the cord circuit with the ground through a test\\'inding 1L1, wound in inductive relation with the secondary winding of the induction-coil associated with-the operators telephone set. Furthermore, it will be seen that the manipulation of the listening-key breaks the connection through the supervisory relay between the negative side of the battery 10 and the tip-strand of the cord-circuit. Thus. while the tip of the calling-plug is normally maintained at a potential equal to that of the negative side of the battery 10, upon the manipulation of the listening-key the part of the tipstrand of the cord-circuit leading to the tip-contact of the calling-plug 23 is connected through the testwinding L1 directly with the ground, to which is connected the positive side of the battery 10. Thus the tip-contact when applied to a test-thimble to ascertain the condition of a tested line is always at the zero potential of the ground. It will be remembered that in case the line to substation B is not busy or has not been called by an operator at some other position the test-thimbles are also at the Zero potential of the ground. Thus upon contact being made between the tip of the calling-plug and the test-thimble there is no difference of potential to cause a current to How. Therefore there is no current-flow through the testwinding 1-1 or a condenser-discharge to cause a click in the operators receiver. which click, as is well understood by those skilled in the art, is commonly employed to notify the operator ot' the busy condition of a line. If, on the other hand, the tested line is connected with a cord-circuit at some operators position, then the test-thimbles associated with that line will have been raised in potential above that of the ground. Therefore upon contact being made between the test-thimble and the tip-contact of the calling-plug a current will be caused to flow through the tipstrand of the cord-circuit and the connected test-winding T1 to the grounded side of the battery 10. The flow of current through the testwinding 41 of course produces a click in the operators telephone, notifying her of the busy condition of the tested line.

\Vhile I have herein shown and described one particular embodiment of my invention,

it will be apparent to those skilled in the art that many modifications therein may well be employed without departing from the spirit of my invention. I do not, therefore, wish to limit myself to the precise disclosure herein set forth; but,

Having described my invention, I claim as new and desire to secure by Letters Patent 1. In a telephone-exchange system, the combination with a common source of current at the exchange, of'a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cut-off relay having two differential windings serially included in one limb of said line, and a testcontact connected to the common terminal of the windings of said differential cut-off relay.

2. In atelephone-exchange system, the combination with a common source of current at the exchange, of atelephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cut-off relay having two differential windings permanently serially included in one limb of said line, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an actuation thereof, and a test-contact connected to the common terminal of the windings of said differential cut-off relay.

3. In a telephone-exchange system, the combination with a common source of' current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cut-off relay having two differential windings serially included in one limb of said line, means whereby the connection of' said cord connecting apparatus with saidline closes a circuit of decreased resistance through one winding of said cut-ofi relay to cause an actuation thereof, and a testcontact connected to the common terminal of the windings of said differential cut-off relay.

4. In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cut-ofi relay having two differential windings permanently serially included in one limb of said line, and a test-contact connected to the common terminal of the windings of said differential cut-off relay.

5. In atelephone-exchange system, the combination with a common source of current at the exchange, one terminal of said source being permanently connected to ground, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cut-off relay having two difl'erential windings serially included in the limb of said line connected to the grounded side of said source of current, and a test-contact connected to the common terminal of the windings of said diiferential cut-off relay.

6. In a telephone-exchange system, the combination with a common source of current at the exchange, one terminal of said source being permanently connected to ground, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, acut-off relay having two differential windings permanentlyserially included in the limb of said line connected to the grounded side of said source of current, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an actuation thereof, and a test-contact connected to the common terminal of the windings of said differential cut-off relay.

7. In a telephone-exchange system, the combination with a common source of current at the exchange, one terminal of said source being permanently connected to ground, of a telephone-line extending by its limbs from the terminals of' said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another f'orconversation, a cut-off relay having two differential windings serially included in the limb of said line connected to the grounded side of said source of current, means Whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an actuation thereof, and a test-contact connected to the common terminal of the windings of said differential cut-off relay.

8. In atelephone-exchange system, the combination with a common source of current at the exchange, one terminal of said source being permanently connected to ground, of a telephone-line extending by its limbs from the terminals of said source of current toa substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cut-off relay having two differential windings permanently serially included in the limb of said line connected to the grounded side of said source of'current, and a test-contact connected to the common terminal of the windings of said differential cut-ofi' relay.

9. In a telephone-exchange system, the combination with a common source of' current at the exchange, of' a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs. cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cutoff relay having two differential windings permanently serially included in one limb of said line, a line-relay permanently serially included in the other limb of said line, a line-signal jointly controlled by said line and cut-off relays, means whereby the connection of said cord connecting apparatus with said line closes a circuit of' decreased resistance through one winding of said cut-off relay to cause an actuation thereof, and a test-contact connected to the common terminal of' the windings of said differential cut-off relay.

10. In a telephone-exchange system, the combination with a common source of' current at the exchange. of' a telephone-line extending by its limbs from the terminals of said source of' current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cutoff relay having two differential windings serially included in one limb of' said line, a linerelay serially included in the other limb of' said line, a line-signal jointly controlled by said line and cut-off relays, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of' said cut-off relay to cause an actuation thereof, and a test contact connected to the common terminal of' the windings of said differcntial cut-off relay.

11. In a telephone-exchange system, the combination with a common source of' current at the exchange, of a telephone-line extending by its limbs from theterminals of' said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cutoff relay having two differential windings permanently serially included in one limb of' said line, a line-relay permanently serially included in the other limb of' said line, a line-signal jointly controlled by said line and cut-off relays, and a test-contact connected to the common terminal of' the windings of' said differential cut-off relay 12. In a telephone-exchange system, the combination with a common sou rce of' current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cutoff relay having two differential windings serially included in one limb of said line, a linerelay serially included in the other limb of said line,a line-signal jointly controlled by said line and cut-off relays, and a test-contact connected to the common terminal of the windings of said differential cut-off relay.

13. In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cutoff relay having two differential windings permanently serially included in one limb of said line, means whereby the connection of said cord connecting apparatus with said line closes a circuit of' decreased resistance through one winding of said cut-off relay to cause an actuation thereof, a test-contact connected to the common terminal of the windings of' said differential cut-off relay, and switching means controlled by said cut-off relay adapted upon an actuation of said relay to connect said testcontact to a limb of said line through a low-resistance circuit in shunt of one winding of said cut-off relay.

11L. In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals ofsaidsource of current to a substation, means at the substation adaptcd to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cutoff relay having two differential windings serially included in one limb of' said line, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of' said cut-off relay to cause an actuation thereof, a test-contact conncctedto the common terminal of the windings of said differential cut-off relay, and switching means controlled by said cut-off relay adapted upon an actuation of said relay to connect said test-contact to a limb of said line through a low-resistance circuit in shunt of one winding of said cut-off relay.

15. In a telephone-exchange system, the combination with a common source of current at the exchange, one terminal of said source being permanently connected to ground,of a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cut-off relay havingtwo differential windings permanently serially included in the limb of said line connected to the grounded side of said source of current, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an. actuation thereof, a test-contact connected to the common terminal of the windings of said differential cutoff relay, and switching means controlled by said cut-off relay adapted upon an actuation of said relay to connect said test-contact to a limb of said line through a low-resistance circuit in shunt of one winding of said cut-01f relay.

16. In a telephone-exchange system, the combination with a common source of current at the exchange, one terminal of said source being permanently connected to ground, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at tne substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cut-01f relay having two differential windings serially included in the limb of said line connected to the grounded side of said source of current, means whereby the connection of said cord connecting apparatus with i said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an actuation thereof, a test-contact connected to the common terminal of the windings of said differential cut-off relay, and switching means controlled by said cut-off relay adapted upon an actuation of said relay to connect said test-contact to a limb of said line through a low-resistance circuit in shunt of one winding of said cut-off relay.

17. In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cutofi' relay having two difl'erential windings permanently serially included in one limb of said line, a line-relay permanently serially included in the other limb of said line, a line-signal jointly controlled by said line and cut-off relays, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-01f relay to cause an actuby its limbs from the terminals of said source.

of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cutoif relay having two differential windings serially included in one limb of said line, a linerelay serially included in the other limb of said line, a line-signal jointly controlled by said line and cut-ofl' relays, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an actuation thereof, a test-contact connected to the common terminal of the windings of said differential cut-off relay, and switching means controlled by said cut-off relay adapted upon an actuation of said relay to connect said test-contact toa limb of said line through a low-resistance circuit in shunt of one winding of said cut-oft relay.

19. In a telephone-exchange system, the combination with a common source of current at the exchange, of atelephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cutoff relay having two differential windings permanently serially included in one limb of said line, a line-relay permanently serially included in the other limb of said line, a line-signal jointly controlled by said line and cut-ofl' relays, means whereby the connection of said cord connectingapparatus with said line closes a circuit of decreased resistance through one winding of said cut-oft relay to cause an actufl: tion thereof, a spring-jack having one contact permanently connected with the limb of the line including said line-relay, a test-contact connected to the common terminal of the wind ings of said differential cut-ofl' relay, and switching means controlled by said cut-off relay adapted upon an actuation of said relay to connect said test-contact to the limb of said line including said cut-ofl relay through a lowresistance circuit in shunt of one winding of said cut-off relay.

20. In a telephone-exchange system, the combination with acommon source of current at the exchange, of a telephone-line extending byits limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cutott relay having two difierential windings serially included in one limb of said line, a linerelay permanently serially included in the other limb of said line, a line-signal jointly controlled by said line and cut-ofl' relays,means whereby the connection of said cord connecting apparatus with said line closes a circuito't' decreased resistance through one winding of said cut-off relay to cause an actuation thereof, a spring-jack having one contact permanently connected with the limb of the lineineluding said line-relay, a test-contact connected to the common terminal of the windings of said differential cut-otl relay, and switching means controlled by said cut-ofl' relay adapted upon an actuation of said relay to connect said test-contact to the limb of said line including said cut-off relay through a lowresistance circuit in shunt of one winding of said cut-olf relay.

2]. In a telephoneexchange system, the combination with a common source of current at the exchange. of a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connectingapparatus at the exchange adapted to connect said line with another for conversation, a cut-otf relay having two differential windings permanently serially included in one limb of said line, a line-relay serially included in the other limb of said line, a line-signal jointly controlled by said line and cut-otl relays, means whereby the con nectjon of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-ott' relay to cause an actuation thereof, a springjaclc having one contact permanently connected with the limb of theline including said linerelay, a test-contact connected to the common terminal of the windings of said ditt'erential cut-ott relay, and switching means controlled by said cut-on relay adapted upon an actuation of said relay to connect said test-contact to the limb of said line including said cut-otl' relay through a low resistance circuit in shunt of one winding of said cut-ott' relay.

2). la a telephone-exchange system, the

combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connectingapparatus at the exchange adapted to connect said line with another for conversation, a cut-off relay l having two differential windings permanently serially included in the other limb of said line. a line-signal jointly controlled by said line and cut-ott relays, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-ott' relay to cause an actuation thereof. a spring-jack having one contact connected with the limb of the line including said line-relay, a test-contact connected to the common terminal of the windings of said ditierential cutott relay, and switching means controlled by said cut-ofi rc lay adapted upon an actuation of said relay to connect said test-contact to the limb of said line including said cu t-otl' relay through a lowresistance circuit in shunt of one winding of said cut-ott relay.

23. In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connectingapparatus at the exchange adapted to connect said line with another for conversation, a cut-off relay having two ditterential windings serially included in one limb of said line, a line-relay serially included in the other limb of said line, a line-signal jointlycontrolled by said line and cut-off relays, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-oll' relay to cause an actuation thereof, a spring-jack having one contact permanently connected with the limb of the line including said line-relay, a test-contact connected to the common terminal ot' the windings of said dill'erential cutoff relay, and switching means controlled by said cut-otl relay adapted upon an actuation of said relay to conncctsaid test-contact to the limb of said line including said cut-ol'l' relay through a low-resistance circuit in shunt of one winding of said cut-oll' relay.

2%. In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephonedine extending by its limbs from the terminals of said source of current to a substation. means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cutotf relay having two dil'l'ereutial windings serially included in one limb of said line, a line relay pernninently serially included in the other limb of said line, a line-signal jointly controlled by said line and cut-otl relays, means whereby the COI'lllOCtlOI] of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-otl' relay to cause an actuation thereof, a spring-jack having one contact connected 1 with the limb of the line including said linerelay, a test-contact connected to the common terminal of the windings of said differential cut-ofi relay, and switching means controlled by said cut-olf relay adapted upon an actuation of said relay to connect said test-contact to the limb of said line including said cut-off relay through a low-resistance circuit in shunt of one winding of said cut-off relay.

25. In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a cutoff relay having two differential windings serially included in one limb of said line, a liner elay serially included in the other limb of said line, a line-signal jointly controlled by said line and cut-off relays, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-ofl' relay to cause an actuation thereof, a springjack having one contact connected with the limb of the line including said line-relay, a testcontact connected to the common terminal of the windings of said differential cut-off relay, and switching means controlled by said cut-off relay adapted upon an actuation of said relay to connect said test-contact to the limb of said line including said cut-off relay through a lowresistance circuit in shunt of one winding of said cut-off relay.

26. In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the central exchange adapted to connect said line with another for conversation, a cutoff relay having two difl'erential windings serially included in one limb of saidline, means whereby the connection of said cord connection apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an actuation thereof, a test-contact normally connected with one limb of the telephone-line through one of said windings, and an armature for said cut-off relay adapted upon actuation of said relay to connect said test-contact directly with said limb.

27. In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the central exchange adapted to connect said line with another for conversation, a cut-off relay having two differential windings serially included in one limb of said line, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an actuation thereof, a test-contact normally connected with one limb of the telephone-line through one of said windings, and means upon connection of said cord connecting apparatus with said line for directly connecting said test-contact with said limb.

28. In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the central exchange adapted to connect said line with another for conversation, a cut-off relay having two differential windings serially included in one limb of said line, means whereby the connection of said cord connection apparatus with said line closes a circuit of decreased resistance through one winding of said cut-ofl' relay to cause an actuation thereof, a test-contact normally connected with one limb of the telephone-line through one of said windings, means upon connection of said cord connecting apparatus with said line for directly connecting said test-contact with said limb, and a line-relay permanently included in the other limb of said line.

29. In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connection apparatus at the central exchange adapted to connect said line with another for conversation, a cut-off relay having two diiierential windings serially included in one limb of said line, means whereby the connection of said cord connection apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an actuation thereof, a test-contact normally connected with one limb of the telephone-line through one of said windings, an armature for said cutoff relay adapted upon actuation of said relay to connect said test-contact directly with said limb, and a line-relay permanently included in the other limb of said line.

30. In a telephone-exchange system, the combination with a common source of current at the exchange, of atelephone-line extending by its limbs from the terminals of said source to a substation, means at the substation adapted to close an electrical connection between said limbs, cord connecting apparatus at the cut-ofl' relay to cause an actuation thereof, a l

test-contactnormally connected with one limb of the telephone-line through one of said windings, a line-relay permanently included in the i ential windings o't said cut-ofl relay, means other limb of said line, two armatures for said cut-ofi' relay and an armature for said linerelay, a local line-signal circuit adapted to include said line-relay armature and one of said cut-ott-relay armatures, and means upon connection of said cord connectingapparatus with said line for causing actuation of said cut-off relay to attract its armatures, whereby said local circuit is opened by one of said cut-oil'- relay armatures and whereby said other cut-- otf-relay armature closes a short circuit about said winding, whereby said test-contact is connected directly with the line-limb.

31. In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, switching mechanism at the substation adapted to close a circuit through said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, at line relay permanently serially included in one limb of said line and controlled by switching mechanism at the substation, a cut-ofi' relay having two difierential windings permanently serially included in the other limb of said line, a line-signal jointly controlled by said lineand cut-otf relays, a spring-jack having a contact permanently connected with said first limb, and a test-contact permanently connected with the common terminal of the ditlerential windings of said cut-ott' relay, means whereby the insertion of a plug of said cord connecting apparatus in said spring-jack closes a circuit of decreased resistance through one winding of said cut-ofi' relay to cause a net energization and actuation thereof, and switching means controlled by said cut-off relay adapted upon a net energization of said relay to connect said test-contact to a limb of said line through a low-resistance circuit in shunt of one winding of said cut-ofl' relay.

32. In a telephone-exchange system, the combination with a common source of current at the exchange having one terminal permanently connected to ground, of a telephoneline extending by its limbs from the terminals of said source of current to a substation, switching mechanism at the substation adapted to close a circuit through said limbs, cord connecting apparatus at the exchange adapted to connect said line with another for conversation, a line-relay permanently serially included in the line-limb which is connected with the terminal of the common source of current not connected to the ground and controlled by switching mechanism at the substation, a cutoff relay having two ditl'erential windings permanently serially included in the other limb of said line, a line-signal jointly controlled by said line and cut-otf relays, a spring-jack having a contact permanently connected with said first limb, and a test-contact permanently connected with the common terminal of the differwhereby the insertion of a plug of said cord connectingapparatus in said spring-jack closes a circuit of decreased resistance through one winding of said cut-otf relay to cause a net energization and actuation thereof, and switching means controlled by said cut-ofi' relay adapted upon a net energization of said relay to connect said test-contact to a limb of said line through a low-resistance circuit in shunt of one winding of said cut-ofl relay.

In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source to a substation, cord connecting apparatus at the exchange for connecting said line with another, a cut-oti' relay having two ditferential windings serially included in one limb of said line, an armature for said relay, a spring-jack contact permanently connected directly with one limb of said line, a test-contact normally connected with the other limb of said line through one of said relay-windings, and means upon connection of said cord connecting apparatus with said line for causing attraction of said armature to cause a short circuit about said winding to connect said test-contact directly with said other limb.

3a. In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source to a substation, cord cormecting apparatus at the exchange for connecting said line with another, a cut-off relay having two differential windings 1.)ermanently serially included in one limb of said line, an armature for said relay, a spring-jack contact permanently connected directly with one limb of said line, a test-contact normally connected with the other limb of said line through one of said relay-windings, and means upon connection of said cord connecting apparatus with said line for causing attraction of said armature to cause a short circuit about said winding to connect said testcontact directly with said other limb.

In a telephone-exchange system, the combination with a common source of current at the exchange, of a telephone-line extending by its limbs from the terminal of said source to a substation, cord connecting apparatus at the exchange, a cut-ofl' relay permanently serially included in one limb of said line, a spring jack contact permanently connected directly the Winding, whereby said test-contact is con with one limb of said line, a test-contact pernected directly with said other limb. 1O manently connected With the other limb of said In Witness whereof I hereunto subscribe my line through part of. said relay-winding, an name this 31st day of January, A. D. 1903. armature for said relay, and means upon con- HARRY Gr. \VEBSTER. nection of said cord connecting apparatus with WVitnesses:

said line for causing attraction of said arma- H. F. DAVIDSON,

ture to close a short circuit about said part of LEE WV. SINCLAIR. 

